Spasmodic dysphonia (SD) remains a controversial and enigmatic disorder of communication. Our goal is to further elucidate and characterize the mechanisms, lesions and etiologies underlying SD. This project is extended to encompass other disorders with one similar compelling feature, a significant dysfunction in vocal motor control. Stuttering has been selected, because, like SD, neuropathology is unknown. Dysarthria of speech of cortical origin has been selected to represent a known lesion. A comparison/contrast approach will provide greater insight into SD and the other disorders than is possible when each is studied alone. It will also increase the understanding of mechanisms of normal speech production. We will evaluate and relate the peripheral motor manifestations of the three disorders to the identified CNS dysfunction. The neurophysiologic test battery includes well known methods of auditory, visual and somatosensory evoked potentials, and ENG. Newer technological advances, such as magnetic resonance imaging, electrocortical topographic measures, and regional cerebral blood flow, will be used. Each measure has been chosen to provide a systems analytic approach to understanding the neural dysfunction in vocal motor control disorders. The design was created to simultaneously achieve two goals: 1) to distinguish the presence of either an anatomic or systems disorder and 2) to evaluate a vertical hierarchy of nervous system function, particularly of motor, auditory and somatosensory systems. Commonalities and differences among the three subject groups will be investigated. Of particular interest is the relationship between auditory system abnormalities and vocal motor control disorders.